**5. Conclusions**

The key to the performance of an ADRC is whether the extended state observer can accurately estimate the state variables of the system. There is a cross-coupling term in the state equation of the asynchronous motor in the synchronous rotating coordinate system. The control of the torque component and the excitation component of the motor stator current will affect each other, thus further affecting the dynamic and static performances of the system.

Actual systems always have unknown dynamic characteristics, i.e., the uncertainty of the model. In the control system, there are often various external disturbances, such as the control quantity disturbance or the measurement noise. LESOo regards the coupling of the dynamic model of the asynchronous motor system as a part of the total disturbance of the system. The disturbance is added to the input of the system model using feedforward compensation. After compensation, the model of the controlled asynchronous motor is transformed into the integrator series type.

The key to the motor speed regulation lies in the regulation of the electromagnetic torque. The improved LESOo had a higher observation accuracy, the estimated value of total disturbance was closer to the real value, the coupling degree between the torque component and excitation component was smaller after compensation, and the improved LESOo could control the torque component more independently; therefore, the control effect of the motor speed was better. Theoretical analysis and simulation results showed that the control effect of the improved LADRC was better than that of the traditional LADRC.

**Author Contributions:** C.W. was responsible for the theoretical analysis and simulation, and wrote the first draft of the paper. X.Z. and Y.M. provided theoretical guidance and content revision. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was funded by the National Natural Science Foundation of China (no. 51877152) and the Natural Science Foundation of Tianjin of China (no. 18JCZDJC97300).

**Acknowledgments:** Thanks to X.Z. and Y.M. for their theoretical guidance during the writing of this paper.

**Conflicts of Interest:** The authors declare no conflict of interest.
